Detection of Escherichia coli using CMOS array photo sensor-based enzyme biochip detection system

This work presents optical enzyme detection system based on the CMOS array photo sensor and 1 × 3 polymeric enzyme biochip for detecting Escherichia coli in a one-step procedure. This assay, using 4-methylumbelliferyl-β-d-glucuronide (MUG) as a fluorogenic substrate, had a detection limit of 0.1 U/ml for β-glucuronidase (GUD), which was approximately equal to a cell concentration of 10⁶ CFU/ml of E. coli. MUG was incorporated into lauryl tryptose broth at a final concentration of 100 μg/ml for immediate verification of the presence of E. coli in 1 × 3 polymeric enzyme biochip. The 40 strains of E. coli studied all produced GUD. Of another 36 strains of bacteria tested, one strain (Salmonella choleraesuis subsp. choleraesuis) yielded very small amounts of GUD after 24 h incubation. The optical enzyme detection system was sensitive and rapid.     

Use of electronic nose technology for identifying rice infestation by Nilaparvata lugens

Plant-emitted volatiles can change after herbivore attack. Monitoring the change in volatile profiles can offer a non-destructive method for determining plant health. An electronic nose (E-nose) equipped with a headspace sampling unit was used to discriminate between volatile profiles emitted by uninfested rice plants and those emitted by rice plants exposed to different numbers of Nilaparvata lugens adults. Principal component analysis (PCA) and linear discriminant analysis (LDA) were used to investigate whether the E-nose was able to distinguish among the different pest treatments. The results indicate that it is possible to separate differently treated rice plants using E-nose signals. The stepwise discriminant analysis (SDA) and a 3-layer back-propagation neural network (BPNN) were developed for pattern recognition models. Calculations show that the discrimination rates were over 92.5% for the training data set and 70% for the testing set using SDA. The correlation coefficient between predicted and real numbers of the pest was found to be over 0.78 using BPNN. Moreover, gas chromatography–mass spectrometry (GC–MS) analysis confirmed the E-nose results. These studies demonstrate that the E-nose technology has clear potential for use as an effective insect monitoring method.     

A photoluminescence-based quantum semiconductor biosensor for rapid in situ detection of Escherichia coli

This work describes a novel method of detecting Escherichia coli using photoluminescence (PL) emission from III–V quantum semiconductor (QS) devices functionalized with two different antibody-based architectures. The first approach employed self-assembled monolayers of biotinylated polyethylene glycol thiols to immobilize biotinylated antibody via neutravidin. In the second approach, we used QS microstructures coated with a thin layer of Si₃N₄ allowing direct functionalization with E. coli antibodies through hydrofluoric acid etching and glutaraldehyde-based reticulation. Atomic force, optical and fluorescence microscopy measurements were used to assess the immobilization process. Depending on the biosensing architecture, density of the immobilized bacteria was observed in the range of 0.5–0.7 bacteria/100 μm². The detection of E. coli at 10⁴ CFU/ml was achieved within less than 120 min of the bacteria exposure. It is expected that an even better sensitivity threshold could be achieved following further optimization of the method.     

Decision tree approach for classification and dimensionality reduction of electronic nose data

This paper presents a decision tree approach using two different tree models, C4.5 and CART, for use in the classification and dimensionality reduction of electronic nose (EN) data. The decision tree is a tree structure consisting of internal and terminal nodes which process the data to ultimately yield a classification. The decision tree is proficient at both maintaining the role of dimensionality reduction and at organizing optimally sized classification trees, and therefore it could be a promising approach to analyze EN data. In the experiments conducted, six sensor response parameters were extracted from the dynamic sensor responses of each of the four metal oxide gas sensors. The six parameters observed were the rising time (T_r), falling time (T_f), total response time (T_t), normalized peak voltage change (y_p,n), normalized curve integral (C_I), and triangle area (T_A). One sensor parameter from each metal oxide sensor was used for the classification trees, and the best classification accuracy of 97.78% was achieved by CART using the C_I parameter. However, the accuracy of CART was improved using all of the sensor parameters as inputs to the classification tree. The improved results of CART, having an accuracy of 98.89%, was comparable to that of two popular classifiers, the multilayer perceptron (MLP) neural network and the fuzzy ARTMAP network (accuracy of 98.89%, and 100%, respectively). Furthermore, as a dimensionality reduction method the decision tree has shown a better discrimination accuracy of 100% for the MLP classifier and 98.89% for the fuzzy ARTMAP classifier as compared to those achieved with principle component analysis (PCA) giving 81.11% and 97.78%, and a variable selection method giving 92.22% and 93.33% (for the same MLP and fuzzy ARTMAP classifiers). Therefore, a decision tree could be a promising technique for a pattern recognition system for EN data in terms of two functions; as classifier which is an optimally organized classification tree, and as dimensionality reduction method for other pattern recognition techniques.     

Optimal (N,T)-policy for M/G/1 system with cost structures

In this paper, the optimal (N,T)-policy for M/G/1 system with cost structure is studied. The system operates only intermittently. It is shut down when no customers are present. A fixed set-up cost of K>0 is incurred each time the system is reopened. Also, a holding cost of h>0 per unit time is incurred for each customer present. The (N,T)-policy studied for this system is as follows: the system reactivates as soon as N customers are present or the waiting time of the leading customer reaches a predefined time T (see A.S. Alfa, I. Frigui, Eur. J. Oper. Res. 88 (1996) 599-613; Y.N. Doganata, in: E. Arikan (Ed.), Communication, Control, and Signal Processing, 1990, pp. 1663–1669). Later on, as a comparison, the start of the timer count is relaxed as follows: the system reactivates as soon as N customers are present or the time units after the end of the last busy period reaches a predefined time T. For both cases, the explicit optimal policy (N^*,T^*) for minimizing the long-run average cost per unit time are obtained. As extreme cases, we include the simple optimal policies for N-and T-polices. Several counter-intuitive results are obtained about the optimal T-policies for both types of models.     

Enhanced H2S sensing characteristics of SnO2 nanowires functionalized with CuO

The CuO-functionalized SnO₂ nanowire (NW) sensors were fabricated by depositing a slurry containing SnO₂ NWs on a polydimethylsiloxane (PDMS)-guided substrate and subsequently dropping Cu nitrate aqueous solution. The CuO coating increased the gas responses to 20 ppm H₂S up to 74-fold. The R_a/R_g value of the CuO-doped SnO₂ NWs to 20 ppm H₂S was as high as 809 at 300 °C, while the cross-gas responses to 5 ppm NO₂, 100 ppm CO, 200 ppm C₂H₅OH, and 100 ppm C₃H₈ were negligibly low (1.5–4.0). Moreover, the 90% response times to H₂S were as short as 1–2 s at 300–400 °C. The selective detection of H₂S and enhancement of the gas response were attributed to the uniform distribution of the sensitizer (CuO) on the surface of the less agglomerated network of the SnO₂ NWs.     

Direct electrochemistry of cytochrome c and biosensing for hydrogen peroxide on polyaniline grafted multi-walled carbon nanotube electrode

Cytochrome c (cyt c) was immobilized into a matrix consisting of polyaniline (PANI) and multi-walled carbon nanotubes (MWNT) by a new strategy. First, PANI chains were grafted onto MWNT through electropolymerization. Second, the amine groups in PANI chains were oxidized at an applied potential of +0.80 V to acquire positive charges that would effectively immobilize negatively charged cyt C. The ITO/MWNT-g-PANI(O)/cyt c electrode exhibited a pair of redox peaks with a peak potential separation (anodic to cathodic) of 0.25 V (vs Ag/AgCl) in 0.1 M phosphate buffer (pH 7.0). The results demonstrated that ITO/MWNT-g-PANI(O)/cyt c promoted direct electron transfer between cyt c and electrode with a high electron transfer rate constant (17 s⁻¹). The ITO/MWNT-g-PANI(O)/cyt c electrode catalyzes the reduction of H₂O₂. The ITO/MWNT-g-PANI(O)/cyt c biosensor displays an amperometric response to H₂O₂ with a linear concentration range from 0.5 μM to 1.5 mM (r = 0.99, n = 12), a high sensitivity (32.2 μAm M⁻¹) and fast response (9 s) and detection limit of 0.3 μM (S/N = 3).     

A novel microbial biosensor based on Circinella sp. modified carbon paste electrode and its voltammetric application

Microbial biosensors have been developed for voltammetric determination of various substances. This paper describes the development of a new biosorption based microbial biosensor for determination of Cu²⁺. The developed biosensor is based on carbon paste electrode consisting of whole cells of Circinella sp. Cu²⁺ was preconcentrated on the electrode surface at open circuit and then cathodically detected with the reduction of Cu²⁺. The voltammetric responses were evaluated with respect to percentage cell loading in the carbon paste, preconcentration time, pH of preconcentration solution, scan rate and interferences. The optimum response was realized by biosensor constructed using 5 mg of dry cell weight per 100 mg of carbon paste in pH 5.5 preconcentration solution. Under the optimum experimental conditions, the developed microbial biosensor exhibited an excellent current response to Cu²⁺ over a linear range from 5.0 × 10⁻⁷ to 1.0 × 10⁻⁵ M (r² = 0.9938) with a detection limit of 5.4 × 10⁻⁸ M (S/N = 3). The microbial biosensor had good sensitivity and reproducibility (R.S.D. 4.3%, n = 6). Finally, the applicability of the proposed microbial biosensor to voltammetric determination of Cu²⁺ in real sample was also demonstrated and validated with atomic absorption spectrophotometric (AAS) method.     

基于电子鼻区分三种致病菌的研究

旨在探讨一种快速检测致病菌的电子鼻方法。本研究利用基于金属氧化物传感器的电子鼻技术检测蜡样芽孢杆菌、单增李斯特菌和缓慢葡萄球菌三种致病菌培养液的挥发性代谢产物,结合化学计量学方法主成分分析(PCA)和聚类分析(CA)对电子鼻原始数据进行统计学分析。PCA模式识别结果显示该技术能够很好的将三种细菌在培养液中的挥发性代谢产物图谱进行区分,CA分析进一步显示单增李斯特菌与缓慢葡萄球菌的气味指纹图谱比较接近,而蜡样芽孢杆菌的图谱与它们的差异较大。研究表明该电子鼻技术有望在致病菌快速检测上得到更广泛的应用。     

Environmentally friendly disposable sensors with microfabricated on-chip planar bismuth electrode for in situ heavy metal ions measurement

This paper presents an environmentally friendly disposable heavy metal ion sensor for in situ and online monitoring in the nature and physiological systems. The miniaturized sensor chip consists of a non-toxic microfabricated bismuth (Bi) working electrode that replaces the conventional mercury electrodes, an integrated Ag/AgCl reference electrode, a gold counter electrode, and microfluidic channels. In this work, the electrochemical behavior of the Bi working electrode was characterized in several non-deaerated buffer solutions using cyclic voltammetry. The detection and quantification of Pb (II) and Cd (II) were statically performed using anodic stripping voltammetry inside the microchannels, in the Pb (II) concentration range of 25–400 ppb (R² = 0.991) with limit of detection of 8 ppb for 60 s deposition, and in the Cd (II) concentration range of 28–280 ppb (R² = 0.986) with limit of detection of 9.3 ppb for 90 s deposition. Particularly, the applications of this sensor chip have been reported with the examples of in situ measurement of Cd (II) concentration in soil pore and ground water and online direct measurement of Cd (II) concentration in cell culture media in its native environment.     

Ab initio calculations of NO2 and SO2 chemisorption onto non-polar ZnO surfaces

The authors present an ab initio study of NO₂ and SO₂ chemisorption onto non-polar ZnO and ZnO surfaces with the aim of providing theoretical hints for further developments in gas sensors. From first principles calculations (DFT-GGA approximation), the most relevant surface reduction scenarios are analyzed and, subsequently, considered in the chemisorption study. First, calculations indicate that NO₂ adsorbs avidly onto Zn surface atoms. This is compatible with the oxidizing character of NO₂. Second, results also explain the sensor poisoning by SO₂ adsorption (since this molecule competes with NO₂ for the same adsorption sites) and indicate that poisoning can only be reverted at typical operation temperatures (T ≤ 700 °C) in the case of stoichiometric ZnO surfaces.     

Potentiometric VOC detection in air using 8YSZ-based oxygen sensor modified with SmFeO3 catalytic layer

Potentiometric oxygen sensor was fabricated and applied to detect several volatile organic compounds (VOCs; acetic acid, methylethylketone (MEK), ethanol, benzene, toluene, o- and p-xylene) at sub-ppm levels in the temperatures range of 400–500 °C. The electromotive force (EMF) linearly changed with the logarithm of VOC concentration. Especially for ethanol and MEK, the sensitivity and EMF at 1 ppm were distinctly lowered for the sensor with the SmFeO₃ coated Pt working electrode. It seems that ethanol and MEK were more easily oxidized on the SmFeO₃ surface than the other VOCs. A discriminative detection of ethanol and MEK apart from the others could be achieved with the combination of two types of the sensors, Pt|8YSZ|Pt(ref.) and SmFeO₃/Pt|8YSZ|Pt(ref.).     

(J, J′)-lossless factorization based on conjugation

This paper is concerned with a derivation of the state-space form of the (J, J′)-lossless factorization which contains both the inner-outer factorization and the spectral factorization of positive matrices as special cases. Also, the (J, J′)-lossless factorization gives a unified framework of H^∞ control theory. We use the method of conjugation which makes the derivation much simpler than the previous literature, most of which used the technique of (J, J′)-spectral factorization. A necessary and sufficient condition is represented in terms of two Riccati equations one of which is degenerated.     

On pure H reduced-order dynamic controllers: an erratum

There are at least two approaches advocated to obtain a pure H^∞ reduced-order dynamic controller for a given augmented plant. One approach is to eliminate completely the H² aspect from a standard H²/H^∞ setting. A second approach is to equate the H² aspect with the H^∞ aspect in that same setting. This paper invalidates the first approach but affirms the second approach and produces the correct equations resulting therefrom.     

Identification of β-lactam antibiotics using bioluminescent Escherichia coli and a support vector machine classifier algorithm

We propose the use of bioluminescent whole cell biosensor combined with a pattern classification algorithm to automatically detect and identify β-lactam antibiotic substances. Escherichia coli cells with a plasmid harboring luxCDABE genes under the β-lactam sensitive promoter element are used as sensors. We present experimental measurements of light production of bioluminescent bacteria subject to 11 antibiotic substances. The patterns of measured light production are classified using a support vector machine classifier. The accuracy and reliability of the classification suggests that this method can be used in the future to probe for new antibiotic substances.     

Strongly Hamiltonian laceability of the even k-ary n-cube

The interconnection network considered in this paper is the k-ary n-cube that is an attractive variance of the well-known hypercube. Many interconnection networks can be viewed as the subclasses of the k-ary n-cubes include the cycle, the torus and the hypercube. A bipartite graph is Hamiltonian laceable if there exists a Hamiltonian path joining every two vertices which are in distinct partite sets. A bipartite graph G is strongly Hamiltonian laceable if it is Hamiltonian laceable and there exists a path of length N − 2 joining each pair of vertices in the same partite set, where N = |V(G)|. We prove that the k-ary n-cube is strongly Hamiltonian laceable for k is even and n  2.     

Electrostatic sprayed SnO2 and Cu-doped SnO2 films for H2S detection

This paper presents the ability of electrostatic sprayed tin oxide (SnO₂) and tin oxide doped with copper oxide (1, 2, and 4 at.% Cu) films to detect different pollutant gases, i.e., H₂S, SO₂, and NO₂. The influence of a copper oxide dopant on the SnO₂ morphology is studied using scanning electron microscopy (SEM) technique, which reveals a small decrease in the porosity and particle size when the amount of dopant is increased. The sensing properties of the SnO₂ films are greatly improved by doping, i.e., the Cu-doped SnO₂ films have large response to low concentration (10 ppm) of H₂S at low operating temperature (100 °C). Furthermore, no cross-sensitivity to 1 ppm NO₂ and 20 ppm SO₂ is observed. Among the studied films, the 1 at.% Cu-doped SnO₂ layer is the most sensitive in the detection of all the studied gases.     

d-正则(k,s)-SAT问题的NP完全性

研究具有正则结构的SAT问题是否是NP完全问题,具有重要的理论价值.(k,s)-CNF公式类和正则(k,s)-CNF公式类已被证明存在一个临界函数f(k),使得当s≤f(k)时,所有实例都可满足;当s≥f(k)+1时,对应的SAT问题是NP完全问题.研究具有更强正则约束的d-正则(k,s)-SAT问题,其要求实例中每个变元的正负出现次数之差不超过给定的自然数d.通过设计一种多项式时间的归约方法,证明d-正则(k,s)-SAT问题存在一个临界函数f(k,d),使得当s≤f(k,d)时,所有实例都可满足;当s≥f(k,d)+1时,d-正则(k,s)-SAT问题是NP完全问题.这种多项式时间的归约变换方法通过添加新的变元和新的子句,可以更改公式的子句约束密度,并约束每个变元正负出现次数的差值.这进一步说明,只用子句约束密度不足以刻画CNF公式结构的特点,对临界函数f(k,d)的研究有助于在更强正则约束条件下构造难解实例.     

Differential pulse voltammetric determination of N-acetylcysteine by the electrocatalytic oxidation at the surface of carbon nanotube-paste electrode modified with cobalt salophen complexes

The preparation and electrochemical performance of the carbon nanotube-paste electrode modified with salophen complexes of cobalt(III) perchlorate, with various substituents on the salophen ligand, as well as their electrocatalytic activity toward the oxidation of N-acetylcysteine (NAC) is investigated. Several Schiff base complexes containing various nucleophilic and electrophilic functional groups were prepared, and their electrochemical characteristics for the electro-oxidation of NAC were evaluated using cyclic and differential pulse voltammetry (CV and DPV). The results revealed, the modified electrodes show an efficient and selective electrocatalytic activity toward the anodic oxidation of NAC among biologically important compounds in buffered solutions at pH of 7.0. The best voltammetric responses were obtained for a carbon-paste electrode (CPE) modified with a salophen complex containing para-methoxy groups on its salicylaldehyde ring. The analytical response of the modified electrode for response to other sulfhydryl compounds (e.g., cysteine, penicillamine, captopril and mercaptopropionyl glycine) in comparison to NAC was investigated by CV and DPV methods. The DPV method was applied as a sensitive method for the quantitative detection of the trace amounts of NAC. A linear dynamic range from 1 × 10⁻⁷ to 1 × 10⁻⁴ M with calibration sensitivity of 0.0646 μA/μM is resulted for NAC in DPV measurements. The detection limit was 5 × 10⁻⁸ M, which is remarkably lower than those reported previously for NAC using other modified electrodes. The results of voltammetric determinations show a very good reproducibility, and the R.S.D. for the slope of the calibration curve, based on 10 measurements in a period of two months, was <3.9%. The detection system provides very stable electrochemical responses toward NAC, makes it very suitable for using in pharmaceutical and clinical measurements.     

A highly sensitive and fast-responding sensor based on electrospun In2O3 nanofibers

In₂O₃ nanofibers with diameters of around 60 nm have been fabricated by electrospinning with a solution containing both poly (vinyl pyrrolidone) (PVP) and indium nitrate, followed by calcination in air at 700 °C. Without further adding catalysts or doping other metal oxides, the sensor based on the as-prepared indium oxide (In₂O₃) nanofibers showed high response and selectivity, fast response and recovery time towards ethanol gas. The simple preparation and excellent properties significantly advance the viability of electrospun gas sensors.